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General Settings

The following options are available on the General page of the Project Settings dialog.

Analysis Type

There are two general types of models which can be created and analyzed in RS2:

PLANE STRAIN

In most cases your RS2 model will represent a Plane Strain analysis. A Plane Strain model assumes that the excavations are of infinite length in the out-of-plane direction, and therefore the strain in the out-of-plane direction is zero.

AXISYMMETRIC

An Axisymmetric analysis allows you to analyze a 3-dimensional model which is rotationally symmetric about an axis (for example, the end of a circular tunnel). Although the input is 2-dimensional, the analysis results apply to the 3-dimensional problem.

For more information, see the Plane Strain and Axisymmetric Analysis topics.

Solid-Fluid Coupling

This refers to the interaction between fluid pore pressure and solid stresses and deformation.

CONSOLIDATION OPTION: NONE

The default analysis is None (i.e. changes in pore pressure do not affect deformation and changes in loading or deformation do not affect pore pressure). This is the case for a total stress analysis (i.e. deformation is a result of changes in total stress). Note that in RS2 2019, Consolidation Option: None is equivalent to Consolidation Option: Uncoupled from RS2 9.0.

COUPLED ANALYSIS (BIOT)

For a fully Coupled analysis based on Biot theory, you must first enable Transient Groundwater in Project Settings. Then you can choose the Coupled Solid-Fluid analysis option. This is used for time-dependent consolidation analysis problems, in which changes in pore pressure can affect deformation and changes in loading or deformation can affect pore pressure.

See the Coupled Consolidation document in the theory section for more information.

Note: Coupled analysis cannot be used in conjunction with Dynamic analysis.

UNCOUPLED ANALYSIS

This analysis type improves the stability and the speed of consolidation analyses. First, at the beginning of the stage, an undrained simulation will be conducted to compute the excess pore pressure. Next, a transient groundwater analysis will be carried out to obtain pore pressure dissipation. Finally, another solid analysis will be carried out to calculate the change in the stress caused by the changes in pore pressure.

If the Use Effective Stress Analysis check box is selected (on the Stress Analysis page of the Project Settings dialog), then deformation is a result of changes in effective stress. This is a partially coupled analysis where changes in pore pressure, and thus effective stress, affect deformation but changes in deformation or loading do not affect pore pressure.

APPLY VISCOUS PROPERTIES

Checking the "Apply Viscous Properties" box turns on associated Material Properties in the Material Properties dialog. Under the Stiffness tab, users can select the Visco-Elastic option when the "Apply Viscous Properties" setting has been turned on in Project Settings.

Solver Type

The Solver Type determines how Compute solves the matrix representing the system of equations defined by your model. Three methods are available:

  • Gaussian Elimination
  • Conjugate Gradient Iteration
  • Pre-Conditioned Conjugate Gradient Iteration

The default method is Gaussian Elimination, but note:

  • For solving large problems, you may have to use one of the Conjugate Gradient solution techniques, since disk swapping (swapping between disk and memory during the analysis) is enabled with the Conjugate Gradient methods. Disk swapping is NOT available with Gaussian Elimination.
  • If all your materials are Elastic, the solution time will be faster with the Conjugate Gradient techniques.

Stress Units

A variety of metric and imperial measurement units are available in RS2. The units used for a model are determined by selecting the desired unit of stress measurement in the Project Settings dialog. You may select one of the following options:

  • Metric units (stress) - MPa, kPa, tonnes/m2
  • Imperial units (stress) - ksf, psf, tons/ft2

All input parameters in the program (e.g. material properties, field stress) will correspond to the selected stress measurement unit. The units of length, force, stress and unit weight are indicated in the Project Settings dialog, just below the Units drop-list.

NOTE: Whenever the Unit system is changed in the Project Settings dialog, the currently selected units automatically become the default Unit system for all NEW files.

Time Units

The Time Units are only applicable for finite element groundwater analysis / consolidation analysis, and determine the following:

  • The Time Units used to define stages for a transient groundwater analysis.
  • The Time Units used for time dependent output quantities such as discharge velocity and flow rate through discharge sections. This is applicable for both steady state and transient groundwater analysis.

You may choose from seconds, minutes, hours, days, months or years. Note: for computational purposes, 1 month is assumed to be 1/12 of a year or 365/12 = about 30.4 days.

If you are not performing finite element groundwater analysis, then the Time Units have no effect on input or output data.

Permeability Units

The Permeability Units are applicable if you are performing finite element groundwater seepage analysis, either steady state or transient. The available Permeability Units depend on the selection of Stress Units (metric or imperial). The selected Permeability Units determine the units of permeability in the Define Hydraulic Properties dialog.

If you are not performing finite element groundwater analysis, then the Permeability Units have no effect on input or output data.

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